Alright gentlemen, I have a quick question. I have still been practicing on scrap tubing from an old 4130 bike that I hacked up. When I finish a fillet, some areas have a really dark(almost black) area around the joint. It is sparse and usually outside of some of the fluxed area. How does one prevent that from happening? Am I not using enough flux? Or, am I not fluxing enough of the tube? I get it to come off, but it's a bear to remove, usually needing a file.

In other news, this morning I had my "AHH HAA!" moment with my fillets...finally found a nice heat ratio to get more brass in my joints with good penetration =)